Naive people who do not understand bitcoin, use services that take away ownership of coins, like coinbase, circle, etc. because they achieve a few advantages over traditional bank accounts - its fast, no downtime & without limits. Banks are moving towards digitalization all over the world and these advantages will no longer remain so in future if banks decide on getting their game sorted. Then people who see value in using services like coinbase will go away because banks can provide all advantages of coinbase even today if they decide to, but much better.

However, what they can't provide is decentralization & privacy. But people who use coinbase, by virtue of them using it, do not desire decentralization & privacy. Thus, the bitcoin community should not pay attention to these companies or their users (though they might be large in numbers & even be current majority of users) unless decentralization & privacy is no longer desirable in bitcoin.